I would agree with jfrey123, it seems like the risks associated with your product would require some micro testing prior to release from your facility. I've worked in facilities where this system is managed through a "soft" and "hard" hold process. All finished goods are automatically placed on soft hold and kept at the facility while testing is underway. After test results are reviewed an approved by qualified personnel, goods are released from soft hold for distribution. If test results indicate a problem, product is instead moved from the soft hold onto a hard hold. From here the investigation begins into root cause, disposition, etc.
The soft hold system has the advantage of keeping product quarantined while test results come in, while not throwing off the metrics associated with product that has failed specifications.
I believe there are laboratories that offer listeria mono testing via PCR with less than 24 hour turnaround time. A well designed sampling system can also help reduce the amount of product that needs to go on hold when positive results are found.
In this situation I would also agree a recall is needed to further test the lot and start an investigation. For the future, your procedure update of not releasing product until test results confirm food safety will prevent recalls of this nature.